1. Field of the Invention
The present invention relates to an optocoupler such as a solid-state relay, etc., and more particularly to an optocoupler capable of controlling an off-state thereof with a prescribed timing.
2. Description of the Related Art
A conventional solid-state relay 900, as illustrated in FIG. 9, has a structure including: a light emitting element 901 (generally, a GaAs LED or a GaAlAs LED) which converts an electric signal into a light: a light receiving element 902 (generally, a phototriac) which converts a light into an electric signal; a driving triac 903 which is coupled to the light receiving element 902: and a resistance element 904. The driving triac 903 is also coupled to a load 905.
When an input current is applied to the light emitting element 901, the light receiving element 902 is activated and the light receiving element 902 drives the driving triac 903 so that the driving triac 903 is switched over to an on-state.
Once the triac 903 is turned on, even if the input current is turned off immediately afterward, the driving triac 903 maintains the on-state until a load current flowing therethrough reaches a zero value (which is a basic operation of solid-state relays).
One method for activating the solid-state relay 900 involves phase control. As illustrated in FIG. 10A, phase control is realized by adjusting the timing of turning on the driving triac 903 based on the timing of applying the input current, thereby controlling the load current. Arbitrary control of the load current is generally possible depending on the application timing of the input current (FIGS. 10A, 10B and 10C).
Now, consider the case where the load 905 must be activated with a half amount of electric power (FIG. 10B) as compared to that required for a full-phase on-driving mode. Activating the load 905 with the half amount of electric power in comparison to that of the full-phase on-driving mode may be achieved by setting the timing of the input current application, as illustrated in FIG. 10B, so as to occur at phase angles of 90xc2x0 and 270xc2x0 of a load current waveform.
As illustrated in FIG. 11, when the input current is applied, the load current is at a peak. Thus, a substantial inrush current may flow into the solid-state relay 900 immediately after the input current is applied, depending on the type of the load 905, thereby adversely affecting the solid-state relay 900.
Once the driving triac 903 is turned on, even if the input current is turned off immediately afterward, the driving triac 903 maintains an on-state until the load current flowing therethrough reaches a zero value. is As illustrated in FIG. 12, especially in the case of a load which gives rise to a load current whose phase is shifted with respect to the phase of a supply voltage, e.g., an inductive load, a steep voltage is applied to the triac 903 as the triac 903 is turned off. Accordingly, there is a possibility that commutation failure may occur.
As described above, the solid-state relay 900 has characteristics such that once the driving triac 903 is turned on, the driving triac 903 maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore, the problems described above may arise depending on the application timing of the input current or the type of the load.
The conventional solid-state relay 900 is not provided with a function of compulsorily turning off the triac 903 when the ambient temperature rises to an extremely high level. At present. the product safety Is sought more than ever. Accordingly, it is desired that any solid-state relay be provided with a function of turning itself off when any abnormality occurs.
As described above, the solid-state relay 900 has characteristics such that once the driving triac 903 is turned on, the driving triac 903 maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore problems such as an increase in the inrush current, commutation failure, etc., may arise depending on the application timing of the input current, the type of the load, etc.
An optocoupler of the present invention includes a driving triac and at least one normally-on driving element coupled in series to the driving triac, thereby accomplishing objects of the present invention.
The optocoupler may be a solid-state relay.
The driving element may include a MOSFET.
The driving element may include a mechanical relay.
A timing of turning off the driving element may be synchronized with a phase point substantially corresponding to 0 V level of a supply voltage on an output side of the optocoupler.
The driving element may include a light emitting element for controlling the MOSFET. The optocoupler may further include a temperature detecting means coupled to the light emitting element.
The driving element may further include a light emitting element for controlling the MOSFET. The optocoupler may further include a resistance element coupled in series to the light emitting element and the resistance element may have a negative temperature coefficient.
The driving element may further include a first light emitting element for controlling the MOSFET. The optocoupler may include a second light emitting element corresponding to the driving triac and an integrated circuit coupled to the first light emitting element and the second light emitting element. The integrated circuit may have a delay function.
There may be more than one driving triac.
According to one aspect of the present invention, when a solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate a driving triac. When the solid-state relay is turned off afterward, a trigger pulse is applied to a normally-on driving element. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode associated with the light receiving element/driving triac, so as to activate the driving triac. When the solid state relay is turned off afterward at a predetermined time, an input current is applied to the light emitting diode associated with the MOSFET so as to turn off the normally-on MOSFET. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to still another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate the driving triac. When the solid-state relay is turned off afterward at a predetermined time, a trigger pulse is applied to a normally-on mechanical relay. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay.
According to still another aspect of the present invention, it is possible to prevent a steep voltage from being applied to the solid-state relay in the off-state. Accordingly, it is possible to prevent commutation failure from occurring.
According to still another aspect of the invention, by preconditioning the solid-state relay so,that an input current will flow into the light emitting diode (which controls the MOSFET) when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET is turned off, thereby compulsorily turning off the device. Accordingly, it is possible to prevent an abnormal operation of the device at high temperatures, for example.
According to still another aspect of the present invention, by preconditioning the solid-state relay so that an input current sufficient to turn off the normally-on MOSFET will flow into the light emitting diode (which controls the MOSFET) by reducing a-resistance value of the resistance element having a negative temperature coefficient when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET is turned off, thereby compulsorily turning off the device. Accordingly, it is possible to prevent an abnormal operation of the device at high temperatures, for example.
According to still another aspect of the present invention, when a phase control is performed, the solid-state relay can maintain a stable on state during the time delay provided by an integrated circuit. Accordingly, It is possible to facilitate the design of the device by using the integrated circuit.
According to still another aspect of the present Invention, there is provided an optocoupler which is characterized by including a plurality of normally-on driving elements coupled in series to a driving triac.
For example, as shown in FIG. 7, two normally-on driving elements 105 may be coupled in series to the driving triac 103. In this case, one of the normally-on driving elements 105 may be dedicated to the xe2x80x9coff-controllingxe2x80x9d of the device (the term xe2x80x9coff-controllingxe2x80x9d as used herein refers to controlling of an off-state of a device, i.e., turning off a device) and the other may be dedicated to the compulsory shutting off of the device operation when the device is abnormally heated, for example.
As a result, it is possible to realize a device which is capable of being controlled so as to be on/off with a predetermined timing and, moreover, it is possible to compulsorily turn of f the solid-state relay 700 when the solid-state relay 700 is abnormally heated, for example.
Effects of the present invention will be described below.
According to the present invention, there is provided an optocoupler such as a solid-state relay, etc., which can not only be turned on, but also turned off with a predetermined timing. As a result, even in the case of driving the load with a prescribed electric power, it is possible to prescribe the timings of turning on/off the solid-state relay for minimizing an inrush current and preventing commutation failure by adjusting such prescribed timings of turning on/off while performing phase control.
Moreover, when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, it is possible to compulsorily turn off the device, thereby preventing an abnormal operation of the device when the device is heated, for example.
Thus, the invention described herein makes possible the advantages of: (1) providing an optocoupler capable of preventing an increase in an inrush current or commutation failure; (2) providing an optocoupler which can be turned off with a prescribed timing; and (3) providing an optocoupler capable of compulsorily turning itself off when any abnormality occurs, e.g., when an ambient temperature rises to an extremely high level.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.